Help needed setting up accounts from hosted server

I just installed Zimbra and it went very smoothly. I set up two accounts I have with Gmail and they are syncing files well.

My problem is with email from a site hosted by Exabytes. That site will not allow me to forward mail to Gmail. I think that means I need to set up my Zimbra account as IMAP.

I am filling in the blanks the best I know and continue getting an error message: "SSL connection failure. Please check host and port settings." I have used the default port settings and the ones that work well with a different email client.

Could you help me know what I am doing wrong and how to complete the process?